The oxygen concentration in a pressurized airplane is less than at sea level. The Hypoxia Inhalation Test (HIT) is used to determine if a patient with chronic lung disease can tolerate the level of hypoxia likely to be encountered. The authors are from Western General Hospital in Edinburgh.
Commercial airlines have a cabin pressure comparable to the altitude at 8,000 feet (2,438 meters). At this altitude the FIO2 is 15.1% (approximately 14.4 kPa, vs 21 kPa at sea level).
Parameters:
(1) SaO2 on pulse oximetry while breathing room air (FIO2 = 0.21) for 5 minutes
(2) minimum SaO2 during the 20 minute HIT trial (FIO2 = 0.15)
(3) PaO2 after the HIT
(4) PaO2 after breathing supplemental oxygen at 2 liters/min for 20 minutes
SaO2 on room air |
minimum SaO2 during HIT |
PaO2 after HIT |
PaO2 after oxygen |
Interpretation |
< 90% |
NA |
NA |
NA |
unit |
>= 90% |
< 85% |
NA |
< 7.5 kPa |
unfit |
>= 90% |
< 85% |
NA |
>= 7.5 kPa |
fit with oxygen |
>= 90% |
85 - 89% |
>= 7.5 kPa |
|
fit to fly |
>= 90% |
85 - 89% |
< 7.5 kPa |
< 7.5 kPa |
unfit |
>= 90% |
85 - 89% |
< 7.5 kPa |
>= 7.5 kPa |
fit with oxygen |
>= 90% |
>= 90% |
|
|
fit to fly |
where:
• If the minimum SaO2 is < 85% during the HIT, then the test is stopped and supplemental oxygen given. In Figure 1 it mentions that areterial blood gases are taken immediately but there is no mention on how this is used.
• Fit to fly with oxygen indicates that a tank of supplemental oxygen is provided during the flight.
Specialty: Emergency Medicine, Critical Care